Permissions#

Permissions can be used to control what system resources the Node.js process has access to or what actions the process can take with those resources.

  • Process-based permissions control the Node.js process's access to resources. The resource can be entirely allowed or denied, or actions related to it can be controlled. For example, file system reads can be allowed while denying writes. This feature does not protect against malicious code. According to the Node.js Security Policy, Node.js trusts any code it is asked to run.

The permission model implements a "seat belt" approach, which prevents trusted code from unintentionally changing files or using resources that access has not explicitly been granted to. It does not provide security guarantees in the presence of malicious code. Malicious code can bypass the permission model and execute arbitrary code without the restrictions imposed by the permission model.

If you find a potential security vulnerability, please refer to our Security Policy.

Process-based permissions#

Permission Model#

Stability: 1.1 - Active development

The Node.js Permission Model is a mechanism for restricting access to specific resources during execution. The API exists behind a flag --experimental-permission which when enabled, will restrict access to all available permissions.

The available permissions are documented by the --experimental-permission flag.

When starting Node.js with --experimental-permission, the ability to access the file system through the fs module, spawn processes, use node:worker_threads, use native addons, use WASI, and enable the runtime inspector will be restricted.

$ node --experimental-permission index.js
node:internal/modules/cjs/loader:171
  const result = internalModuleStat(receiver, filename);
                 ^

Error: Access to this API has been restricted
    at stat (node:internal/modules/cjs/loader:171:18)
    at Module._findPath (node:internal/modules/cjs/loader:627:16)
    at resolveMainPath (node:internal/modules/run_main:19:25)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:76:24)
    at node:internal/main/run_main_module:23:47 {
  code: 'ERR_ACCESS_DENIED',
  permission: 'FileSystemRead',
  resource: '/home/user/index.js'
}

Allowing access to spawning a process and creating worker threads can be done using the --allow-child-process and --allow-worker respectively.

To allow native addons when using permission model, use the --allow-addons flag. For WASI, use the --allow-wasi flag.

Runtime API#

When enabling the Permission Model through the --experimental-permission flag a new property permission is added to the process object. This property contains one function:

permission.has(scope[, reference])#

API call to check permissions at runtime (permission.has())

process.permission.has('fs.write'); // true
process.permission.has('fs.write', '/home/rafaelgss/protected-folder'); // true

process.permission.has('fs.read'); // true
process.permission.has('fs.read', '/home/rafaelgss/protected-folder'); // false
File System Permissions#

The Permission Model, by default, restricts access to the file system through the node:fs module. It does not guarantee that users will not be able to access the file system through other means, such as through the node:sqlite module.

To allow access to the file system, use the --allow-fs-read and --allow-fs-write flags:

$ node --experimental-permission --allow-fs-read=* --allow-fs-write=* index.js
Hello world!
(node:19836) ExperimentalWarning: Permission is an experimental feature
(Use `node --trace-warnings ...` to show where the warning was created)

The valid arguments for both flags are:

  • * - To allow all FileSystemRead or FileSystemWrite operations, respectively.
  • Paths delimited by comma (,) to allow only matching FileSystemRead or FileSystemWrite operations, respectively.

Example:

  • --allow-fs-read=* - It will allow all FileSystemRead operations.
  • --allow-fs-write=* - It will allow all FileSystemWrite operations.
  • --allow-fs-write=/tmp/ - It will allow FileSystemWrite access to the /tmp/ folder.
  • --allow-fs-read=/tmp/ --allow-fs-read=/home/.gitignore - It allows FileSystemRead access to the /tmp/ folder and the /home/.gitignore path.

Wildcards are supported too:

  • --allow-fs-read=/home/test* will allow read access to everything that matches the wildcard. e.g: /home/test/file1 or /home/test2

After passing a wildcard character (*) all subsequent characters will be ignored. For example: /home/*.js will work similar to /home/*.

When the permission model is initialized, it will automatically add a wildcard (*) if the specified directory exists. For example, if /home/test/files exists, it will be treated as /home/test/files/*. However, if the directory does not exist, the wildcard will not be added, and access will be limited to /home/test/files. If you want to allow access to a folder that does not exist yet, make sure to explicitly include the wildcard: /my-path/folder-do-not-exist/*.

Permission Model constraints#

There are constraints you need to know before using this system:

  • The model does not inherit to a child node process or a worker thread.
  • When using the Permission Model the following features will be restricted:
    • Native modules
    • Child process
    • Worker Threads
    • Inspector protocol
    • File system access
    • WASI
  • The Permission Model is initialized after the Node.js environment is set up. However, certain flags such as --env-file or --openssl-config are designed to read files before environment initialization. As a result, such flags are not subject to the rules of the Permission Model. The same applies for V8 flags that can be set via runtime through v8.setFlagsFromString.
  • OpenSSL engines cannot be requested at runtime when the Permission Model is enabled, affecting the built-in crypto, https, and tls modules.
  • Using existing file descriptors via the node:fs module bypasses the Permission Model.
Limitations and Known Issues#
  • Symbolic links will be followed even to locations outside of the set of paths that access has been granted to. Relative symbolic links may allow access to arbitrary files and directories. When starting applications with the permission model enabled, you must ensure that no paths to which access has been granted contain relative symbolic links.